1. Field of the Invention
The present invention relates to a movable-component linear drive apparatus for linearly moving a movable component, for example, a light source of a scanning device for scanning a subject of photograph with linear light.
2. Description of the Related Art
Heretofore, various radiation-image recording mediums, for recording a radiation image of a subject upon exposure to radiation transmitted through subjects, have been proposed and put into practical use in a variety of fields, including the medical field.
Such radiation image recording mediums include, for example, a radiation image detector using a semiconductor material which develops electric charges upon exposure to radiation, and a stimulable phosphor sheet which accumulates radiation energy upon exposure to radiation and exhibits photostimulated luminescence upon exposure to reading light.
When reading out a radiation image as an electric signal from the aforementioned radiation image recording medium, a reading light source which emits linear reading light is employed from the viewpoint of rapid readout, and the radiation image recording medium is scanned with the reading light by moving the reading light source in a direction substantially perpendicular to the longitudinal direction thereof (see U.S. Pat. No. 6,268,614).
In the present day, from the viewpoint of miniaturization, there has been proposed a cassette, in which the radiation image recording medium as mentioned above and a reading light scanning device including a reading light source are both provided. Using such a cassette allows a radiation image to be read out immediately after the radiation image is recorded by a radiation image recording system. It is also possible to readily record another radiograph image under another imaging condition based on the observation of the read out radiation image.
For a mammographic X-ray system, for example, a cassette position may be varied depending on the imaging conditions when taking radiophotographs. Thus, the reading light source is not limited to be moved horizontally, but may have to be moved in a direction inclined with respect to the horizontal direction.
Accordingly, for example, if the reading light source is moved by means of a motor and the driving current of the motor is optimally selected for horizontally moving the reading light source, when the moving direction of the reading light source is changed to, for example, a vertically rising direction, a shortage of the driving current would be caused since the load, with respect to the motor, increases due to the effect of gravity. This prevents stable movement of the reading light source, which would result in degradation of image quality of the read-out radiation image. On the other hand, if a driving current sufficient for moving the reading light source in the vertically rising direction is always applied in order to avoid the shortage of driving current, when the reading light source is moved horizontally or downward, over-torque is caused immediately after the beginning of the traveling of the reading light source. This also prevents the reading light source from being moved with stability, which would result in degradation of image quality of the read-out radiation image.
The typical methods of overcoming the disadvantages mentioned above include reducing the weight of the reading light source and selecting a motor having an extremely high motor rating, as long as the overall driving load is not affected thereby. However, such reading light sources and such motors are very expensive, thereby increasing the manufacturing cost.
Some radiation image recording systems are designed to perform scanning with reading light while moving the radiation image recording medium without changing the position of the reading light source. Even in such radiation image recording systems, when the moving direction of the radiation image recording medium changes, stable movement of the radiation image recording medium would not be ensured, causing degradation of the image quality of the read out radiation image, as in the case where the moving direction of the reading light source changes.